Gabby Wallace started her Youtube channel back in 2011 as a way of sharing homework materials with students. It petered along for a while, but she started to step up production in late 2014, and managed to grow the channel from about 20k to 100k subscribers in less than 1 year.
Today she runs a 6-figure business selling ESL courses via her youtube channel and her website, GoNaturalEnglish.com, and is launching a new venture to help other online teachers do the same.